Ch11 Test 2 Spring Semester Flashcards
2 tools to control scatter:
Grids
Beam restricting devices
The primary effect in reducing patient doses is:
Proper collimation
3 primary factors that contribute to intensity of scatter:
Kvp
Field size
Patient thickness
Approximately, _____ % of X-rays are incident on th patient to reach the IR
1%
If we increase kvp, we increase scatter which results in _______ contrast.
Decreased
Increased field size results in _______ scatter.
Increased
Increased patient thickness, _______ scatter
Increases
An extremity will be much sharper of an image
The use of a compression device lowers patient dose and also ________ improves.
Spatial and contrast resolution
Image forming X-rays consist of both:
Transmitted(pass thru w/out interaction
Photoelectric absorption
2 devices remove scatter:
Grids
beam restrictors
3 types of beam restrictors:
Aperture diaphragm
Comes/cylinders
Variable aperature collimator
A lead or lead lines metal diaphragm attached to the X-ray tube
Aperture diaphragm
Modification of the aperature diaphragm. An extended metal restricts beam to circular image
Cones/cylinders
Cylinders are most common
Cones used in Dental
Most all machines use this beam restrictor. Has an automatic PBL,
3 mm lead thickness
Variable aperature collimator
Mandated by the us food and drug administration in 1974.
Positive beam limitation
PBL
14x17 to 10x12 ….^ mAs to _______
“…….” to 8x10…….^ mAs to________
“……” to 5x7……….^ mAs to ________
25-35%
40%
60%
The _________ Grid frequency; the _______ your technique
Higher, higher
Moving grids can be either of the 2 types of grids
Parallel or
Focused
With a parallel grid; the biggest disadvantage is
Grid cutoff
Moving Grids can be either of these two:
Reciprocating (back n forth)
Oscillating (circular motion)
The higher the grid ration; the ______ Bucky factor!
Higher
Bucky factor increases with ______ KVP
Increased
We will have ______ grid cutoff with a 5:1 than a 12:1
LESS!!
What does the Bucky factor measure??
Primary radiation
Scatter (secondary) radiation
Image contrast is approximately ______ when grids are used!
Doubled
OD optical density and contrast is
Compton scattering
Transmitted
High Kvp results in
Low kvp results in
Which type of X-ray interaction:
*Increases Compton scatter
Photoelectric decreases
*Photoelectric increases!!
Interspace material (between the lead; the structure) can be what material:
Aluminum
plastic fiber
Aluminum has 2 advantages:
Nonhygroscopic -doesn’t absorb moisture like plastic fiber does
High quality material
Fiber grids are preferred bcuz of lower patient dose.
Aluminum has less visible grid lines but:
Increased patient dose!
4 types of grids:
Parallel
Crossed
Focused
Moving
What does the autotransformer do ?
Kvp selector
Has one winding, one core
Primary and secondary side
Where is the mA meter ?
Secondary winding of the high voltage generator side
What is a rectifier and where is it?
Converts ac-dc
It’s in the high voltage section
(Secondary side)
The release of electrons from getting “boiled off” is called
Thermionic emission
The filament is made of what material ?
Target is made of?
Copper
Tungsten
3 phase, 6 pulse
3 phase, 12 pulse
high frequency
14%
4%
Less than 1%
Single and full wave are 100%
What determines the heat in the filament?
mA
Cloud of electrons is ?
What is the X-ray source?
Space charge
Focal spot
Where is the focusing cup?
Cathode side
Negative charge
When using The heel affect, less radiation is on the anode side. Therefore, place the thicker body on
The cathode side
